Winder

The Winder (小さなキー,Chīsana Kī?, lit. "Tiny Key") or the Wind-Up Key (ねじ巻き,Neji-Maki?) is an item found in Corpse Party and Corpse Party: Book of Shadows. In it's first appearance, is the key to Ayumi and Yoshiki opening up the passageway to the locker room where they find the next ghost tongue.

CHAPTER 4

Yoshiki and Ayumi find the winder under some floorboards in the west hall of the second floor. It is used in the mechanism inside the classroom 1-A to open up a passage to the locker room in the first floor.

The wind-up key is found in the hallway of the second building by Mitsuki and Masato next to a red spirit. The group uses the wind-up key inside the girls' lavatory of the same building. Mitsuki decides to put the wind-up key inside the small hole in on the stall door and turn it which unlocks the door to the entrance of the second building as well as causing an earthquake.

Significant plot details end here.

Trivia

In the game files there's another icon for what seems to be a different wind-up key.